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On retrieving the attached plots, I am at lost to interpret a couple of features,

In the "time series area averaged of cloud fraction from cloud mask" plot, obtained by MODIS-Terra, how is it to be interpreted the sharp increase from 2015 onwards? (it does not show up at all in the equivalent MODIS-Aqua plot).

In the "time series area averaged of combined cloud optical thickness" plot, obtained by MODIS-Aqua, how is it to be interpreted the very marked minima at every February solstice, which appears in the global plot as well as for either hemisphere ? (it does not show up at all in the equivalent MODIS-Terra plot).


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  1. Answer to this question from a Subject Matter Expert at GSFC:


    “The Terra MODIS cloud mask trend: This is due to cross-talk in the several IR spectral channels used in the mask. This is an issue for both Collection 5 (C5) and C6 production streams. We have documented this on our web site under “Data Issues” ( and the accompanying “impact” document link at the bottom of that section) as well as in our L3 time series browse imagery (, click on “cloud fraction”, go to the tropical latitude figure, place the mouse over “Terra”).

    The MODIS MCST group has provided a cross-talk correction that is still being tested by the cloud mask team. Hope to get it into reprocessing early next year.


    ~Jan/Feb minimum in Aqua MODIS cloud optical thickness: Our L3 time series browse imagery shows a cloud optical thickness minimum for the boreal winter months for ice clouds over land for ±60 ° (see link above, click on “cloud optical depth”, go to the ±60° time series). This has the largest annual cycle, i.e., ocean surfaces, liquid phase clouds, and other latitude zones in our browse have a much smaller cycle and are out of phase with the ice cloud time series. The user is looking at combined phase (liquid + ice) and looking at all latitudes/surfaces; this is a dangerous thing to do but I’d say the browse image is consistent.”